Wireless and mobility support issues Georgios Karagiannis Ericsson

Generic handover performance requirements Handover rates –For one application more requests needed than in wired networks Fast reservations: –Slow QoS establishment causes handover delays  Loss of user packets  Minimize RTT during QoS establishment  Handover requests treated with higher priority  Minimize number of bits transmitted over “slow” links Note: using an existing transport protocol below NTLP increases length header

General issues with mobility support Inter-subsystem handover forces mobile node (MN) to change assigned IP address –If flow ID contains IP address and flow ID used for identifying state:  Association between flow ID and state is lost  Use an additional ID to identify NTLP transport state that does not include MN’s IP address and keeps association with flow ID(s) before and after handover

Implications using TCP over 2,5 and 3G wireless networks Latency: high due to extensive processing in physiscal layer Data rates: –for 2,5 G system: 10-20kbs uplink 10-40kbs downstream –For 3G system: 64kbs uplink 384 kbs downlink Asymmetry: asymmetric uplink and downlink data rates Delay spikes: sudden increase in latency of communication path: –Link layer recovery due to temporal loss of coverage –Handover delays

Implications using TCP over 2,5 and 3G wireless networks Packet loss due to corruption –Loss rate of IP packets is low due to link ARQ, but recovery at link layer introduces delay jitter Inter system handovers –Network charectiristics after handover may be different Periodic and frequent allocation and deallocation of resources for each user: –Bandwidth oscillations that affect throughput  These characteristics affect TCP performance:

Implications using TCP over 2,5 and 3G wireless networks  These characteristics affect TCP performance: IETF PILC group studied theimpact and provided recommendations: Examples of recommendations: –Use Selective Acknowledgment option (SACK) –Use TCP time stamp option –Open header compression issues that have to be studied and worked out by IETF ROHC WG related tocompression of handshaking packets and compression of TCP options (SACK, time stamp) Other general remark: Multiple TCP streams are needed between mobile users and network