Singapore and Hong Kong exchange connectivity (SGX, HKEX)

Facts a trading network engineer in Singapore or Hong Kong should know, checked on 2026-10-03 against the exchanges’ own documents (links below). On the Windows machine, local copies of the PDFs are in (local cache, not published) (not committed). Exchange specs change often; re-check versions before relying on a detail.

Why this matters in 2027

Both exchanges are in the middle of platform migrations that land in 2027:

• SGX moves its securities market from REACH-ST to a new trading engine, Iris-ST, with new ITCH and OUCH interfaces, and moves its primary data centre. Mandatory conformance testing runs Jan–Apr 2027.
• HKEX is building the Orion Derivatives Platform (ODP): technical readiness in 2027, market rollout in phases over 2027–2028, with an OMD-D market data interface upgrade and market testing expected in 2027.

Firms trading these markets will spend 2027 on new feeds, new data centre connectivity and testing, so these changes are a natural interview topic for SG/HK roles (my mapping).

SGX

Platforms

• Securities: REACH-ST today, replaced by Iris-ST. “Iris-ST is limited to securities trading, it replaces Reach-ST. Derivatives trading continues in Titan-DT.” Iris-ST is built on Nasdaq Eqlipse and cuts over “big bang”; the old OMnet API is not supported. Source: SGX Iris-ST FAQ v2.1, 31 Jul 2026, questions 1.1, 1.6, 2.3. Checked.
• Derivatives: Titan-DT. SGX announced in December 2014 that its next-generation derivatives trading and clearing systems would be “based on Nasdaq’s Genium INET solution”. Source: GlobeNewswire, 29 Dec 2014. Checked.

Iris-ST timeline (FAQ 2.1, 2.2, 13.3, 12.12; checked): preliminary specs Nov 2025; test environment details Dec 2025; conformance test cases Q4 2026; mandatory conformance testing Jan–Apr 2027; Iris-ST goes live in the new data centre; installation in the new data centre available from Sep 2026.

Market data on Iris-ST (FAQ section 8; checked):

• Feeds: ITCH Market-by-Order (MBO) and ITCH Market-by-Price (MBP), each over multicast or TCP; a FIX market data feed over TCP only (MBP).
• MBP and MBO are separate channels with separate sequence numbers. MBP (and the indicative equilibrium price) has a holdback timer of about 100 ms to limit bandwidth.
• Resilience: “participants can subscribe to both primary and secondary feeds”; a Rewinder fills small gaps; Glimpse gives a snapshot after long disconnections. The Rewinder is multicast-only, so test it with a UDP tool, not telnet (FAQ 11.24).
• Framing: MoldUDP64 headers over multicast, SoupBinTCP over TCP; the message bodies are identical. ITCH has no filtering: you receive the whole channel.
• SGX is “exploring” separate RP IP addresses and source IPs for market data A, B and UAT (FAQ 12.9), so its multicast is PIM-SM with a rendezvous point rather than SSM. Compare CME in ../multicast/00-glossary.md.

Order entry on Iris-ST (checked): new OUCH interface alongside FIX. SGX’s stated benefits of ITCH/OUCH over OMnet are “reduced complexity in API transactions …, improved latency and deterministic performance” (FAQ 6.4). OUCH cannot cancel orders entered through FIX (FAQ 7.2).

Data centres and connectivity (FAQ sections 11–12; checked):

• New primary data centre (PDC); the secondary data centre (SDC) is unchanged and connected by an inter-DC link.
• Trading engine “2+1”: primary and hot standby in the PDC, a third replicated instance in the SDC. The SDC instance supports TCP only.
• Production IP addresses (and some ports) change for every service in the PDC; SDC addresses stay the same.
• From colocation you can take ITCH over multicast or TCP, MBO and MBP at the same time, and FIX order entry over TCP.
• During the migration, a high-capacity link joins the old and new data centres, and test access stays on the old site’s QA handoff.
• Non-colocated members move from MPLS towards IPsec VPN; MPLS QA is not supported for Iris-ST. Telcos are migrated by SGX. On-net carriers are listed at sgx.com; all except GTT and Agora have said they will be in the new data centre.

Titan ITCH and GLIMPSE (derivatives). Source: TITAN ITCH & GLIMPSE Protocol Specifications, release 1.4, 2016-05-10. Checked.

• ITCH is a “multicast stream of Order Book changes” framed with MoldUDP64.
• In MoldUDP64 “each outbound packet is transmitted only once regardless of the number of listeners”. A heartbeat is a packet with a message count of zero. Retransmissions are not multicast: a client re-requests missed messages and the answer comes back to the socket that asked.
• GLIMPSE is a point-to-point snapshot feed (SoupBinTCP).

HKEX

OMD-C, securities market data (checked: HKEX OMD-C page): launched September 2013. Three products: Securities Standard (conflated market-by-price), Securities Premium (streaming market-by-price), Securities FullTick (streaming market-by-order).

How OMD-C delivers and recovers data. Source: OMD-C Developers Guide v1.15, sections 2.2, 5.2.2, 6.1, 6.2; checked.

• UDP multicast, split into channels; “The data on each channel comes from two redundant lines, A and B.”
• Arbitrate, do not fail over. “Clients should not prioritize line A over line B … Line A is not guaranteed to be faster than B … The approach that assumes listening to line B only if there is a gap detected on line A is incorrect.” Gap detection should look only at sequence numbers, not at which line a packet came from. The two lines may package messages into packets differently.
• Heartbeats are packets with message count 0 that do not increase the sequence number.
• Retransmission servers (RTS) over TCP:
  • logon within 5 seconds;
  • they keep only about 50,000 recent messages per stream;
  • one connection per client; at most 1,000 requests a day and 10,000 messages per request;
  • four RTSs (two at the primary site, two at the backup site), all active. “The RTS should not be thought of as a means of recovering intraday.”
• Refresh service: multicast snapshots, for an intraday start, a large gap, a slow RTS or a failed RTS.

Order entry (Unverified): OCG-C (Orion Central Gateway – Securities Market) is HKEX’s access gateway to the securities trading platform (OTP-C), according to press coverage; not yet checked on HKEX’s site.

Colocation (checked: Mondo Visione copy of the HKEX release): HKEX’s data centre in the Tseung Kwan O Industrial Estate opened in January 2013; “Hosting Services occupies two dedicated floors in the Data Centre and can support up to 1,200 racks.”

Orion Derivatives Platform (ODP) (checked: HKEX ODP page and client notice MDD/26/441, 10 Aug 2026):

• Timeline: “materially complete development in 2026”, technical readiness 2027, rollout “2027 and 2028 in phases”. The certification test is targeted to start in 2027.
• Market data: OMD-D gets an interface upgrade (spec version 2.3 in August 2026) and an offline simulator. Clients should develop in 2026 “in preparation for the marketized testing currently expected to take place in 2027”.
• Press reports say ODP replaces HKATS and DCASS (Unverified on HKEX’s own page).

Interview angles (my mapping)

• Design: connect a new firm to SGX Iris-ST market data in the new PDC. Cover cross-connects, primary and secondary feeds on separate paths, PIM-SM with SGX’s RPs, recovery over Rewinder (multicast) and Glimpse (TCP), capture and timestamping, and how you would test in the Jan–Apr 2027 conformance window.
• Why does HKEX say not to prefer line A? Either line can arrive first, and the packets differ, so a feed handler must merge both by sequence number; “use B only on a gap on A” adds latency and loses data. See A/B arbitration in ../low-latency/07-ch07-transport.md.
• Recovery design: why OMD-C’s RTS limits (50,000 messages, 1,000 requests a day) push large-gap recovery to the refresh service.
• Migration planning: production IP and port changes, running old and new data centres side by side, carrier moves, test access during the move.

Self-check

1. What replaces SGX REACH-ST, when is conformance testing, and what happens to production IP addresses?
2. Name SGX’s two ITCH recovery mechanisms and when to use each.
3. What does HKEX’s OMD-C guide say about listening to line B only when line A has a gap?
4. Why should OMD-C clients not use the RTS to recover a large intraday gap?
5. What does SGX FAQ 12.9 suggest about how SGX’s multicast is built?