Mobility and cellular networks
Transcription
Mobility and cellular networks
Wireless WANs Mobility and cellular networks Cellular radio and PCS networks Wireless data networks Satellite links and networks Basic concepts and directions in telecommunications Cellular networks Cellular networks First generation: initially debuted in Japan in 1979, analog transmission system Second generation (2G): introduced digital transmission, operational in 1992 2.5G: offers enhancements to the data services on existing second-generation digital platforms Third generation (3G): digital, permit per-user and terminal mobility, broadband applications (voice, data, and multimedia streams) at higher data speeds 144Kbps to 384Kbps, up to 2Mbps Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 2 C. Courcoubetis Mobility, etc.- 3 Mobile users use for a given time period channels (frequency pairs) to connect to base station Problem: interference from remote stations and users frequencies control channels fixed network Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 4 The concept of a cell The digital cellular architecture Interference: reduced when cells are small (1 / r 2 ) Possibility of frequency reuse Size of cell: function of density of users and of demand, possibility of breaking large cells into smaller ones Need for hand-off Cell 2 Cell 2 Cell 3 Cell 7 Cell 5 Cell 4 Cell 2 Cell 5 Cell 4 Cell 6 Cell 4 Cell 6 Cell 1 Cell 6 Cell 1 Cell 1 Cell 3 Cell 7 Cell 3 Cell 7 Cell 2 Cell 3 Cell 7 Cell 1 Cell 5 Cell 4 Cell 6 A seven-cell cluster variable size cells Cell 5 frequency ruse Cell 1 Cell 2 channels Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 5 The digital cellular architecture (2) Basic concepts and directions in telecommunications TDMA: time slots /frequency channel C. Courcoubetis Mobility, etc.- 6 GSM (2G) GSM supports 124 channel pairs with a 200KHz spacing to prevent channel interference TDM with 8 slots: eight callers per channel Basic GSM: data rates 9.6Kbps International roaming with a single invoice, SIM card security, SMS Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 7 Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 8 GPRS (2G+) GSM evolution Always-on data service, <115Kbps Packets sent over the 8 time slots of GSM More architectural components added to GSM – the Gateway GPRS Service Node (GGSN) gateway between the GPRS network and IP networks, connect to other GPRS networks to facilitate GPRS roaming – the Serving GPRS Service Node (SGSN) The SGSN provides packet routing to and from the SGSN service area for all users in that service area, performs mobility management functions Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 9 GSM – new services, improved quality & performance, lower cost – backward compatibility – independent of UMTS standards GSM phase 2+ – – – – – – – new services (ΙΝ services+) quality equal to fixed network circuit switched data < 76.8 kbps efficient administration (routing, packet data) location services GSM/DECT interworking GPRS: wireless extension of Internet over GSM network WWW, ftp,…, low QoS, combines 1-8 14kbps voice ch. Basic concepts and directions in telecommunications 3G C. Courcoubetis Mobility, etc.- 10 3G (2) 3G is designed for high-speed multimedia data and voice Its goals include high-quality audio and video and advanced global roaming, which means being able to go anywhere and be automatically handed off to whatever wireless system is available (4G?) Objectives: – improve throughput and QoS, voice quality, battery life, positionlocation services – Coexistence with current infrastructures, including backward compatibility, ease of migration or overlay, interoperability and handoffs, the need for bandwidth on demand, improving authentication and encryption methodologies to support mobile commerce (m-commerce) – Supporting higher bandwidths over greater allocations (that is, 5MHz to 20MHz) UMTS is considered the proposed 3G standard towards the IMT2000 Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 11 Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 12 Universal Mobile Telecommunications Systems Goal: remove any distinctions between mobile and fixed networking – supports the ITU's UPT concept: personal mobility across many different networks, each user is issued a unique UPT number UMTS Forum: speedup processes, evolution integrates existing technologies (GSM 2…) proposes new ones global technology concept IP is pushed further into the network – interconnection, charging, security, management, performance – public, business to business, financial, ... – Frequency hopping: 802.11b, Bluetooth – Direct Sequence CDMA: 3G user signals are spread up to a wideband by multiplication by a code power of user wideband signal must be above the rest of the signals in order to be successfully received at the receiver. power DS-CDMA 1 -1 -1 1 -1 -1 1 -1 1 1 -1 1 -1 -1 1 -1 1 1 freq Basic concepts and directions in telecommunications Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 14 UMTS architecture Can we transmit on the same frequency and the same time? Yes, using CDMA: power of one wideband signal – transparency of service access, seamless provisioning, satellite+terrestrial,… Content and value-added services Code Division Multiple Access narrowband signal (i.e. voice call) Mobility Basic services Mobility, etc.- 13 C. Courcoubetis – low cost of new technologies – open architectures Telecommunications UMTS: a whole system, not just technologies Basic concepts and directions in telecommunications Personal communications in the 21st century Universality – personal mobility, smart cards, Virtual Home Environment, service mobility, personal service profile – regulatory framework, spectrum, standards – the example of GSM – – – – The UMTS vision New elements – UMTS 99: RNC, Node B (WBTS) – UMTS R4:MSC Server, Media Gateway (MGW) – UMTS R5: all IP network -1 1 -1 -1 1 -1 1 1 1 -1 1 1 -1 1 -1 -1 C. Courcoubetis Mobility, etc.- 15 Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 16 UMTS architecture Circuit core Convergence of technologies Initial implementation PSTN BS SGSN IP GGSN Packet core PSTN BS SGSN GGSN R5 and beyond IMS (IP) IMS IP Packet core Mobility, etc.- 17 C. Courcoubetis Next Generation Networks Transition from single-service networks to multi-service networks In NGN service intelligence is decoupled from network transmission Offers converged services: fixed telephony, mobile telephony, broadband Internet, leased lines, … Traffic from various access networks types is aggregated: fixed (ISDN, FTTx), mobile (PLMN), wireless (802.1x), … Core network is IP-based Supports QoS (G/MPLS) Basic concepts and directions in telecommunications Content C. Courcoubetis – GPRS (GSM phase 2+, point-to-point-multi-point connectionless, connection-oriented, IP service, tunneling), WAP – ATM – TCP (wireless case, new proposals: link-layer forward error corrections, end-to-end Selective ACKs, splitconnection, Snoop protocol), QoS enhancements – mobility management (MIPv6++) – addressing issues The purpose is service continuation regardless of user’s place and client capabilities. IP Basic concepts and directions in telecommunications Combine elements from 2G: GSM, IP, ATM Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 18 IMS - IP Multimedia Subsystem Content Servers Communcation Control IP Core Network Access Access Access Access Access Access 3GPP (3rd Generation Partnership Project) is working on IMS – 3G Release 5 – A commercial step towards NGN – Enables services that are independent from access network technologies – Based on Internet protocols – 4G? 3 layer architecture Clients Mobility, etc.- 19 – Transport (networking fabric & gateways) – Control (signaling elements) – Services (back end systems & content) Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 20 IMS and mobility IMS Main Components SIP is the protocol used for session management Users have a public SIP address (identifier) [email protected] Mobility is enabled through proxy servers and registrars – Proxy servers process/forward requests from users and other proxies – A registrar stores information about users (IP address of user’s terminal or current proxy server) “Home provider” has control on services received from roaming user, as he participates in authentication and performs authorization, accounting in order to bill A 4G-provider is expected to be a 3G provider that can interoperate with other 3G providers during the provision of a single service Basic concepts and directions in telecommunications Mobility, etc.- 21 C. Courcoubetis Example of a session between 2 roaming users in IMS A’s visited network Required on registration, optional on session establish GPRS Home Subscriber Server (HSS): a database with subscriber information Basic concepts and directions in telecommunications Visited 200 OK network REG P-CSCF 200 OK REG I-CSCF Home REG 200 OK network S-CSCF C. Courcoubetis Mobility, etc.- 22 BT Fusion The first commercially available service bringing Fixed-Mobile Convergence (since fall 2005) BT decides the most appropriate access network for delivering services, based on subscriber’s location S-CSCF I-CSCF P-CSCF I-CSCF SIP Optional voice packets B’s visited network User B I-CSCF GPRS I-CSCF B’s home – Proxy CSCF: UE’s first point of contact (can be either on the visited or home network) – Interrogating CSCF: a type of “proxy” for incoming SIP requests from other networks – Serving CSCF: session controller assigned to subscriber (always on the home network) A’s home network User A S-CSCF Registration example Call Session Control Function (CSCF): Set of entities for managing user sessions Required on registration, optional on session establish P-CSCF – 3 choices in case of telephony services: POTS, VoIP, Mobile – Combines functionality of a mobile phone with reliability of fixed telephony and/or lower charges (especially for VoIP) Vodafone is the associated mobile operator network Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 23 Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 24 Content strategies BT Fusion User owns a special access point and a dual-mode handset User is assigned only one identifying number (from BT) Calls routed to fixed-line network within range of Bluetooth access point (WiFi in future) – VoIP if quality is acceptable, POTS otherwise – more profit for the provider – traditional strategy of cable operators & cellular providers Out of range calls routed to cellular network BT has full control (not the user)! An open access portal model allows the user unrestricted access to whatever content is available. Cellular network Convergent Handset PSTN Cell site Fusion Access Point Bluetooth or WiFi – based on the “End-to-end” principle of Internet – network operators charge purely on traffic (bit pushers) PSTN Link NTE Broadband Link OR Basic concepts and directions in telecommunications A walled garden is a mechanism for a provider to restrict the user experience by confining the user to a specific region/space as defined by the provider VoIP Gateway ADSL NTE C. Courcoubetis Mobility, etc.- 25 Basic concepts and directions in telecommunications C. Courcoubetis Mobility, etc.- 26