Transcript Wireless and mobility support issues

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